This invention relates to an apparatus for use in controllably injecting contaminants into a liquid flowing in a system.
The nature and concentration of contaminants found in service are infinite and therefore to provide a common and representative base for evaluating cleaning devices, artificial contaminants or test dust of a known and fixed composition are employed. The contaminant removal efficiency of the cleaning devices may then be determined by introducting, into the liquid flow, artificial contaminants in prescribed concentrations. This requires an apparatus which will inject the artificial contaminant in controlled amounts and, at the same time, achieve complete dispersion of the contaminant in the flowing liquid.
There are specifications available which outline test procedures for evaluating cleaning devices including the type of test dust and contaminant injection rate to employ. There are a number of existing techniques used to introduce a contaminant, such as powder, into a liquid which include mechanical, ultrasonic or mechanical spreader mixing followed by forced injection of the contaminant into the liquid. In mechanical mixing, solid particles are mixed with a liquid in a reservoir using a rotor resulting in a slurry which is then forced into the liquid stream of a test system by way of a pump. In ultrasonic mixing the rotor is replaced by an ultrasonic agitator. The mechanical spreader technique consists of dropping the solid particles onto a variable speed driven belt where they are then evenly spread. The particles are then dumped into a reservoir and mechanically mixed as a slurry which is pumped into the liquid stream. Another technique is referred to as air entrainment in which the solid particles are entrained and conveyed to the point of injection by air. The dust cloud is then bubbled through the liquid. In what is known as erosion and turbulent mixing, the flowing liquid erodes away that part of the test dust which is in contact with the liquid. If the liquid has enough turbulence, the eroded chunks are broken away and a reasonably homogeneous mixture may be obtained.
There are limitations in using the foregoing techniques. For example, in mechanical mixing followed by forced injection, although control over the injection may be relatively good, it is difficult to determine the exact quantity injected in most cases. Also the solid particles enter the liquid as a slurry and not in a fully dispersed state. Furthermore, the apparatus must be cleaned to ensure contamination build up does not occur in the injection system, affecting the performance of the device. Generally, the mechanical equipment must be fairly complex to provide the desired operation.
With ultrasonic mixing and forced injection, what is stated above with respect to the drawbacks of mechanical mixing also applies and there is an additional problem in that ultrasonic agitation is normally not sufficient to keep the heavy particles of contaminants in suspension. Mechanical spreader and forced injection systems require relatively complex mechanical equipment and also the contaminant enters the liquid stream as a slurry and it is difficult to determine the exact quantity injected. In the case of air entrainment, the contaminant must be in the form of a dry powder and as a result there is a tendency for the larger and heavier contaminant particles to be entrained last. Also, deposits of contaminant build up at the point of injection because the liquid stream dampens the dust causing it to coalesce and deposit there. With erosion and turbulent mixing, although the contaminant enters the liquid stream in a well dispersed manner, the injection rate is very difficult to regulate. The rate fluctuates markedly during any single injection and is virtually impossible to repeat.
For effective comparison in the performance of cleaning devices and also to reasonably predict their performance in service, the artificial contaminant should be representative of the contaminant in size, distribution, density and shape factor found in service. The rate of which the contaminant is fed into the test circuit should be completely controlled and the test dust should enter the flowing liquid in a finely divided and dispersed state.
A principal object of the present invention is to provide an injection apparatus that will accomplish the foregoing which has the capability of introducing both large and small quantities of contaminant materials.
A further principal object of the present invention is to provide an injection apparatus that is simple in operation, easy to install in a test system and yet have no effect on the performance of the cleaning device being tested.
It is a further object of the present invention to provide an injection apparatus which is as self-contained as possible and requires minimum capital, operating and maintenance costs.